With both William and the princess-to-be feeling pre-wedding jitters, this run-through is one of several rehearsals planned before the big day. Next up: Middleton's sister and bridesmaid Pippa, 27, will likely join some of the wedding party for a run-through at the Royal Mews, where the horses and carriages are kept.

Also gearing up for the big day by putting in prep time Thursday: the Household Cavalry, who will be on-guard for the ceremony.